Spinning of acrylonitrile polymers



Oct. 9, 1951 SPINNING OF ACRYLONITRILE POLYMERS V 7 Filed June 17, 1950 DlSSOLVlNG-- SPINNING SOLUTION MAKE-UP TANK t SPIN TROUGH A COOLING GOOLING FILTERING ETHYLENE OARBONATE PRECIPITATE FILTRATE INVENTOR GERALD A. Mc FARREN ATTORNEY G. A. MCFARREN 2,570,257

Patented Oct. 9, 1951 UNITED STATES PATENT OFFICE SPINNING OF ACRYLONITRILE POLYMERS Gerald A. McFarren, Bay Village, hio,'assignor to Industrial Rayon Corporation, Cleveland, Ohio, a corporation of Delaware Application June 17, 1950, Serial No. 168,837

(Cl. l8-54) 20 Claims. 1

This invention relates to a process for producing shaped articles such as fibers, ribbons, films, etc. by wet spinning ethylene carbonate spinning solutions of acrylonitrile polymers and copolymers. More particularly, this invention is concerned with a continuous wet-spinning process capable of being operated efliciently for prolonged periods of time without sacrificing uniformity, color or other desirable physical properties of the spun articles. More specifically, it is concerned with conducting a continuous wet-spinning process in whichthe ethylene carbonate solvent is continuously and efllciently recovered and re-used and the coagulating bath continuously regenerated with a minimum loss of solvent and coagulant materials.

In the wet spinning of ethylene carbonate spinning solutions of acrylonitrile polymers, there is a continuous accumulation of ethylene carbonate dissolved in the coagulating bath which, if excessive, will adversely affect not only the continuity of the spinning process but also will affect the character of the spun articles, hereinafter referred to sometimes as fibers. It is found necessary, therefore, either to continuously discard portions of the bath while continuously replenishing fresh coagulant, or, preferably, to remove and recover for re-use the excess quantities of ethylene carbonate from the used bath liquid and return the reclaimed coagulant to the coagulating bath.

With regard to the latter method of spin-bath regeneration, it has been found that fractional distillation of spin bath liquid containing ethylene carbonate cannot be accomplished completely satisfactorily in most cases even under vacuum because of one or more of the following reasons: (a) excessive decomposition of the ethylene carbonate by alcoholysis, resinification, etc. takes place during fractional distillation which substantially decreases the yield of the recovered ethylene carbonate; (b) the decomposition products which are carried over into the operating bath promote the discoloration of the filamentary material being formed therein; (0) such decomposition products in the bath promote further decomposition ofthe ethylene carbonate by alcoholysis, etc. during extrusion and coagulation in the bath.

Thus, for example, if a used spinning bath liquid containing about 15% by weight ethylene carbonate and about 85% by weight glycerol is distilled in vacuum at 5-10 m. m. of mercury to fractionate out the ethylene carbonate, very little of the ethylene carbonate distllls over. In-

stead, an almost complete alcoholysis and breakdown takes place leading to the formation of ethylene glycol and glycidol. Losses of a similar nature but to lesser extent are experienced when fractionating ethylene carbonate from baths consisting of alkylene glycols or polyalkylene glycol ethers such as, for example, Z-methylpentanediol- 2,4, diethylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol, etc.

By the process of the present invention, not only are the above difficulties in the wet spinning of ethylene carbonate solutions of acrylonitrile polymers substantially eliminated, but an efficient, continuous spinning process is provided by which fibers having desirable properties and appearance are produced with facility and efficiency.

The accompanying drawing is a schematic representation of the process conducted in accordance with the invention.

In accordance with the present invention, a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least by weight of acrylonitrile and ethylene carbonate as the solvent for such polymer is wet-spun by the following process: The ethylene carbonate spinning solution is extruded into a liquid coagulating bath medium comprising ethylene carbonate and a water-soluble, liquid, aliphatic polyhydric alcohol compound to form the spun article. At least a portion of the'used bath liquid is cooled to precipitate the ethylene carbonate therefrom and the precipitated ethyllene carbonate thereafter separated from the cooled liquid. The resulting treated liquid from which ethylene carbonate has been removed is recycled in controlled quantities to the operating coagulating bath to regenerate the same as desired and the wet-spinning cycle repeated. Advantageously, the removed precipitate is also recycled for re-use in preparing additional polymeric spinning solutions. In general, a suflicient quantity of used bath liquid is removed for treatment and a suflicient quantity of the resulting treated liquid is returned to the bath so as to maintain the operating bath at the desired ethylene carbonate concentration. Advantageously, the concentration of ethylene carbonate in the coagulating bath is maintained between about 10% and 30% by weight.

In practicing this invention, the portion of the coagulating bath removed for treatment and recovery is cooled to a temperature below that at which the ethylene carbonate precipitates therefrom but above the concealing point of the polyhydric alcohol compound in the bath liquid.

The liquid coagulating medium employed in accordance with the present invention as indicated above comprises ethylene carbonate and a water-soluble, liquid, aliphatic polyhydric alcohol compound. Among such polyhydric alcohol compounds may be mentioned the alkyleneglycols', e. g., ethylene glycol, propylene glycol, 1,4-butyl ene glycol, 2-methylpentanediol-2,4, or the polyalkylene glycol ethers, e. g., diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, etc., or'othe'r polyhydric alcohol compounds, c. g., glycerol, thiodiethylene glycol, etc. Particular advantages are derived, however, by employing a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2 methylpentanediol-2,4, and mixtures of these glycols. Of these, dipropylene glycol is particularly suitable and especially advantageous.

Advantageously, the coagulating medium employed should contain, exclusive of the ethylene carbonate therein, a major proportion by weight of the polyhydric alcohol compounds. Thus, the coagulating medium may contain minor quantities of other materials or impurities dissolved or suspended therein such as, for example, minor amounts of water, e. g., water due to the hygroscopicity of the polyhydric alcohol. In eneral, the less the amount of such other materials in the coagulating medium, the more beneficial and advantageous are the results. Thus, particularly advantageous results are derived when the coagulating medium, exclusive of the ethylene carbonate therein, contains at least about 70% by weight of the polyhydric alcohol compound, and preferably when it consists essentially of the polyhydric alcohol compound. In general, dissolved liquid materials in the bath, other than the ethylene carbonate and the polyhydric alcohol compounds, may be tolerated in amounts up to about 20% to 25% by weight of the polyhydric alcohol coagulant without undue adverse afiect upon the spinning process. In this respect, it is noteworthy that the amount of such extraneous materials in an operating coagulating bath usually will diminish after several cycles of recovery and purification of the coagulant as hereinafter described with the result that the coagulating bath liquid will usually improve in efliciency with use.

As stated above, at least a portion of the used bath liquid is cooled to precipitate the ethylene carbonate therefrom. This precipitation is ac ,complished by cooling the portion undergoing treatment to a temperature below that at which the ethylene carbonate precipitates therefrom but above the congealing point of the polyhydric alcohol compound therein. Advantageously, a used bath liquid containing between 10% and 30% ethylene carbonate may be cooled to a tem perature between about 10 C. and -20 C. to obtain satisfactory precipitation. In general, greater economies and efficiencies are effected when the upper range of precipitation temperatures, e g., between about C. and l0 C., are employed providing of course, that satisfactory yields of precipitate are obtained. The lower range of cooling temperatures may be employed where higher yields of ethylene carbonate precipitate are desired providing, however, that the polyhydric alcohol coagulant is not too viscous at such lower temperatures. Thus, when using .a polyhydric alcohol compound such as, for example, Z-methylpentanediol-ZA, propylene glycol,

from av cooled bath liquid is removed from the liquid phase by any convenient method such as,

for example, by filtering or with greater advantage by centrifuging the resulting slurry to extract most of the liquid from the ethylene carbonate solids. Advantageously, the extraction of the solids may be carried out so that the solids contain less than about 15% by weight of the adherent bath liquid, particular advantages being derived, however, at less than about 10% and especially at less than about 5%. This may be accomplished with advantage by centrifuging the slurry sharply under a centrifugal force of fore than about 200 G with a cake thickness on the wall of the centrifuge between about onefourth inch and four inches. By the expression 200 G is meant 200 times the force of gravity or 200 times the force required to accelerate a body about 980 cm./sec./sec. Especial advantages, however, are derived when the centrifuging is carried out under a centrifugal force between about 500 G and 2000 G with a cake thickness between about one-half and three inches. The centrifuging time under these conditions may range between about 30 seconds and 20 minutes depending upon the sizeof the ethylene carbonate crystals and upon the type of filter screen employed in the centrifuge. I

The separated and extracted ethylene carbonate precipitate may be re-used directly to prepare additional quantities of the polymer spinning solution, or if desired, the precipitate may be additionally purified such as, for example, (a) by washing with cold carbon tetrachloride or ice water, (b) by recrystallization from ice water, (0) by distillation under reduced pressure, or (d) by treatment with decolorizing carbon. Thus, particular advantages are'derived, for example, when the precipitate obtained by filtration of the slurry, e. g. by centrifuging, is rinsed briefly with a small amount of ice water at between about 0 C. and 5 C. and the residual water in the precipitate flashed off. Even greater advantages are derived in the way of purity and color when the precipitate is distilled under vacuum prior to recycling the same for reuse inthe preparation of additional polymeric spinning solution.

As previously stated, the treated liquid which remains behind after the removal of the ethylene carbonate precipitate from the slurry, is recycled to the operating coagulating bath in controlled quantities sufficient to maintain the concentration of the ethylene carbonate in the operating coagulating bath between about 10% and 30% by weight. If desired, the liquid to be recycled may, with advantage, be filtered prior to its introduction into the operating bath. Since a bath which is recycled and re-used repeatedly in accordance with the present process tends to discolor eventually and since impurities tend to form and accumulate therein during spinning, it is found advantageous to further treat part or all of the filtrate liquor at intervals to remove such impurities. Thus, for example, a portion of the filtrate liquor may be by-passed and heated occasionally in the presence of small quantities of decolorizing carbon for about 5 to 30 minutes at 60 to C. and the resulting decolorized liquor then returned to the operating bath. In addiv parts and percent by weight.

Example I 20 parts of polyacrylonitrile (average molecular weight about 42,000) is dissolved in 80 parts ethylene carbonate. This solution after filtering and deaerating under vacuum, is heated to 120 C. and extruded through a spinneret having 40 holes (.003 inch diameter) into a coagulating bath consisting of 80 parts dipropylene glycol and 20 parts ethylene carbonate. The bath temperature is maintained at 130 C. while the coagulated filaments are drawn through the bath for 30 inches of bath travel and then collected on bobbins rotating at a peripheral speed of about 44 meters per minute. The yarn is then washed, stretched and relaxed to produce a final product which is very light colored and of uniform quality having a. soft, silky feel, a denier of about 94, and a breaking tenacity of about 4.4 grams per denier and a breaking elongation of about 18%.

A 500 gram portion of the operating bath is cooled to and maintained for about 2 hours at C. to complete the precipitation of the ethylene carbonate. The resulting slurry is then centrifuged for 15 minutes in a perforated cylindrical basket about inches in diameter and about 2 /8 inches in height. The interior of the perforated basket is lined with-a metal cloth having a 55 x 60 mesh twill weave. The basket is spun at about 3000 R. P.- M. (640XG). [CF=0.0000142(dia) (R. P. M0 where the diameter is the diameter of the basket in inches and CF is the centrifugal force in G5; CF=0.0000142(5) (3000) The thickness of the caked precipitate is about inch. The yield of the recovered ethylene carbonate is approximately 60% and has a purity of about 90%. The recovered ethylene carbonate is used to dissolve additional quantities of the polymer to form more spinning solution. The filtrate is returned to the bath in controlled quantities to maintain the operating bath at the above operating concentration, and the cycle is then repeated.

- Example II The procedure of this example is the same as Example I except for the following: The operating coagulating 'bath consists of 78 parts dipropylene glycol and 22 parts ethylene carbonate. The bath portion removed for treatment is cooled to 9 C. The resulting slurry is centrifuged for l5'minutes with the basket spinning at about 3800 R. P. M. (920XG) and having a cake thickness of about one inch. The yield of the recovered ethylene carbonate is about 50% and has a purity of about 91%.

Example III The procedure of this example is the same as Example I except for the following: The operating coagulating: bath consists of 82 parts dipropylene glycol and 18 parts ethylene carbonate. The bath portion removed for treatment is cooled to 5 C. The resulting slurry is centrifuged forlil minutes with the basket spinning at about 6 3600 R. P. M. (920XG) and having a cake thickness of about inch. The yield of the recovered ethylene carbonate is about 60% and has a purity of about 92%.

' Example IV The purity of the recovered ethylene carbonate of Examples I, II and III is improved. by rinsing the cake in the rotating basket with water at between about 0 C. and 5 C. After centrifuging for an additional time to allow for the removal of the water, the cake is removed from the centrifuge and the residual water removed therefrom by a flash distillation operation at about 60 m. in. pressure and at about 45 C. The purity of the resulting carbonate is about 95 Example V The recovered ethylene carbonate from Examples I, II and III after the purification of Example IV is decolorized by heating to about 0., adding to the resulting solution about 0.5% of decolorizing carbon and stirring for about 15 minutes. The charcoal is then filtered from the heated solution and the decolorized solution is returned for use in preparing the spinning solution. The filtrates of Examples I, II and III are also decolorized by adding about 1% by weight decolorizing carbon to the filtrate maintained at about C. and stirring. The resulting carbon slurry is filtered and the filtrate is returned to the operating coagulating bath.

Example VI The procedure of this example is the same as Example I except for the following: The portion of the operating bath removed for the recovery treatment is decolorized prior to the cooling step by adding to the hot bath liquid about 1% decolorizing carbon and stirring for about 10 minutes. The carbon is removed by filtering and the bath portion is then cooled to permit precipitation of the ethylene carbonate therefrom.

Example VII The procedure of this example is the same as Example I except for the following: About 45 pounds of the operating bath liquid is removed and cooled to 10 C. The resulting slurry is then transferred to a centrifuge similar to but larger than that of Example I and having a basket about 12 inches in diameter and about 5 inches in height. The transfer of the slurry is performed in 2 minutes while the basket is rotated at about 1300 R. P. M. forming a cake in the basket having a thickness of about 1 M inches. The speed of the basket is then increased to 2750 R. P. M. (1200 G) and maintained at this speed for about one minute. The resultingfiltrate is set aside for purification prior to recycling the same to the bath. Thereafter, the rotating cake is rinsed with about one pound of water at between 0 C. and 5 C., the rinsing step being performed in about one minute. The increased speed.

' distilled therefrom at a temperature of 45 C. at

60 m. m. pressure. Thereafter, the ethylene carbonate is distilled at 10 m. m. pressure and between and 118 C. The resulting distilled ethylene carbonate is a colorless product and has a purity of about 97%. This material is then used to dissolve additional quantities of polyacrylonitrile polymer to form the spinning solution employed. The filtrate obtained from the centrifuging of the cooled slurry,

7 is heated to and maintained at 80 C. for about -15 minutes while stirring and admixing about 0.5% by weight of decolorizing carbon The resulting mixture is then filtered to remove the carbon and the filtered liquid returned in controlled quantities to the operating bath.

Example VIII Theprocedure of this example is the same as Example I except for the following: The coagulating bath consists of 85 parts 2-methylpentane diol-2,4 and 15 parts ethylene carbonate. A 200 gram portion of the operating bath is cooled-to and maintained at l C. for about one hour and then centrifuged for 5 minutes. The yield of the recovered ethylene carbonate is approximately 75% and has a purity of about 90% Example IX The procedure of this example is the same as Example I except for the following: The coagulating bath consists of a mixture of 38 parts propylene glycol, 38 parts dipropylene glycol and 24 parts ethylene carbonate. The bath portion is cooled to -15 C. The yield of the recovered ethylene carbonate is about 75% and has a purity of about 91%.

Example X I Example XI The procedure of this example is the same as Example I except for the following: The coagulating bath consists of '78 parts of a mixture of dialkylene glycols and 22 parts ethylene carbon ate; The mixture of dialkylene glycols contains approximately 75% dipropylene glycol, diethylene glycol and ethylene-propylene diglycol HOCH2CH2OCHz--CHOHCH3, The

yield of the recovered ethylene carbonate is about 60% and has a purity of about 90%. Di-

alkylene glycol mixtures of this type are available commercially such as, for example, Dicol produced by the Wyandotte Chemicals Company.

Emample X] I -bath may be either decolorized or filtered or both as in Example V1 prior to the crystallization step. Likewise, such used bath liquid may be treated so as to increase the concentration of ethylene carbonate therein and thereby enhance the yield of recovered ethylene carbonate.

Among the polymers and copolymers containing at least-80% acrylonitrile which may be employed in accordance with the process of this invention may be mentioned polyaci'ylonitrile and copolymers of acrylonitrilewith the following monomeric compounds: vinyl esters '(vinyl acetate, vinyl formate, vinyl 'benzoate), vinyl ethers. and vinyl ketones; acrylic acid and its esters and amides; methacrylic acid and its esters, amides, and nitrile; maleic, itaconlc', fumaric, crotonic acids and their esters, amides and nitriles; allyl alcohol and'its esters; styrene and nuclear substituted styrenes, e. g. chloroand dichloro styrene; halogenated monoethylenic compounds such as vinyl chloride. vinyl fluoride, and vinylidene chloride; N-vinyl compounds such as N-vinyl pyrrolidone, N-vinyl succinimide, N-vinyl carbazole, 2- and 4-vinylpyrid'ine; and the like.

For various purposes it may be desirable to chemically and physically modify ,the polymeric compositions of this invention by the presence of other materials such as, torexample, pigmerits, dyes, plasticizers, color stabilizers, spinning agents. etc.

The acrylonitrile polymers and copolymers may be prepared by any suitable polymerization method such as, for example, the ammonium persulfate catalyzed polymerization of I monomer or monomers dissolved or dispersed in water. Molecular weights of these polymers and copolymers are preferably within the range of 10,000 and 250,000, or even higher, although polymers having molecular weights between 30,000 and 150,000 may be used with particular advantage in the production of fibers.

In general, the spinning solutions may be prepared by heating a mixture of "the finely divided acrylonitrile polymer or copolymer with the ethylene carbonate solvent until the polymer is dissolved. Advantageously, the spinning solution may be maintained, prior to extrusion, at temperatures between about and 150 C., and preferably between about and 120 C. These spinning solutions, preferably, should have a. solids content between about 15% and 30% solids depending upon the molecular weight of the polymer, and preferably between about 18% and In general, in the preparation. of spinning solutions with recovered and recycled ethylene'carbonate according to the present process, it ,is advantageous to employ the ethylene carbonates of higher purity with the more difllculty soluble polymers and copolymers. Thus, when employing polyacrylonitrile or copolymers containing more than about 95% acrylonitrile, it is preferable that the recycled ethylenecarbonate contain less than about 10% by weight of the co-' agulating liquid and with especial advantage less than about 5%. On the other hand with copolymers containing between about 80% and acrylonitrile, the lower purity carbonates, for example, those containing between about 10% and 15% of the coagulating liquid, can be used with similar success.

The freshly coagulated materials withdrawn from the'coagulatin bath of the present process may be washed with an aqueous media such as water, and thenstretched up to 600-1000 percent or more. The stretching may be accomplished in secondary baths containing materials similar to those suitable for use in the coagulating baths of thzs invention, or if desired. in other heated media such as, for example, inert liquids, vapors or gases, e. g. steam. The stretched products may be heat treated while in a relaxed condition 9 at temperatures between about 100 and 180 C. to improve their physical properties.

I claim:

1. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium comprising ethylene carbonate and a water-soluble, liquid, aliphatic polyhydric alcohol compound; cooling at least a portion said liquid coagulating medium to a temperature below that at which the ethylene carbonate precipitates therefrom but above the congealin point 01' the polyhydric compound; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; separating the precipitated ethylene carbonate from the cooled liquid; returnin at least a portion of the resulting liquid to said coagulating medium; and repeating the cycle.

2. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate therein, contains a major proportion by weight of a water-soluble, liquid, aliphatic polyhydric alcohol compound; cooling at least a portion of said liquid coagulating medium to a temperature below that at which the ethylene carbonate precipitates therefrom but above the congealing point of the polyhydric compound; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; separating the precipitated ethylene carbonate from the cooled liquid; returning at least a portion of the resulting liquid to said coagulating medium; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form therein, contains at least about 70% by weight of a water-soluble, liquid, aliphatic polyhydric alcohol compound, said coagulating medium containing between about and by weight of ethylene carbonate; cooling at least a portion of said liquid coagulating medium to a temperature below that at which the ethylene carbonate precipitates therefrom but above the congealing point of the polyhydric compound; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; separating the precipitated ethylene carbonate from the cooled liquid; returning at least a portion of the resulting liquid to said coagulating medium: dissolving additional quantities of said polymeric materal with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

4. In the process of producing shaped articles from a polymeric spinning olution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by-weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate '1 in said precipitate; returning at least a portion of the resulting liquid to said liquid coagulating medium; dissolving additional-quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

5. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, contains at least about by weight of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2- methylpentanediol-2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulating medium to a temperature below that at which the ethylene carbonate precipitates therefrom but above the congealing point of the glycol compound; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; separating the precipitated ethylene carbonate from the cooled liquid; returning at least a portion of said resulting liquid to'said coagulating medium; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

6. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, consists essentially of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2-methylpentanediol- 2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulating medium to a temperature between about 10 C. and 20 (3.; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; separating the precipitated ethylene carbonate from the cooled liquid; returning at least a portion of said resulting liquid to said coagulating medium; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle. i

7. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule'at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, consists essentially of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2-methylpentanediol- 2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulating medium to a temperature between about 10 C. and 20 0.; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; extracting the coagulating liquid from said separated precipitated ethylene carbonate until less than about 10% by weight of said coagulating liquid remains in said precipitate; returning at least a portion of the resulting liquid to said coagulating medium; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

8. A process according to claim 7 in which the glycol compound is dipropylene glycol.

9,. A process according to claim '7 in which the glycol compound is propylene glycol.

10. A process according to claim 7 in which the glycol compound is tripropylene glycol.

11. A process according to claim 7 in which the glycol compound is 2-methylpentanediol-2,4.

12. A process according to claim '7 in which the glycol compound is a mixture of said glycol compounds, dipropylene glycol being present in a major proportion of said mixture.

13. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning, solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, consists essentially of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, tri ethylene glycol, tripropylene glycol, Z-methylpentanediol-2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulating medium to a temperature between about 10 C. and -20 C.; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; extracting the coagulating liquid from said separated precipitated ethylene carbonate until less than about by weight of said coagulating liquid remains in said precipitate; returning at least a portion of the resulting liquid to said coagulating medium; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

14. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, consists essentially of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2-methyl pentanediol-2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulating medium to a temperature between about 10 C. and 20 C.; precipitating at least a Portion of the ethylene carbonate present in said cooled liquid; centrifuging the resulting mixture until the precipitate contains less than about 10% by weight of said cooled liquid; returning at least a portion of the resulting liquid to said coagulating medium; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

15. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least 80% by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, consists essentially of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2-methylpentanediol-2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulatingmedium to a temperature between about 10 C. and -20 C.; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; centrifuging the resulting mixture under a centrifugal force above about 200 G; maintaining the precipitate in said centrifuge at a thickness between about one-fourth inch and four inches; returning a quantity of the resulting liquid to said coagulating bath sufiicient to maintain the concentration of ethylene carbonate therein between about 10% and 30% by weight; dissolving additional quantities of said polymeric material with said separated ethylene carbonate to form said spinning solution; and repeating the cycle.

16. A process according to claim 15 in which i the glycol compound is dipropylene glycol.

1'7. A process according to claim 15 in which the glycol compound is a mixture of said ycol compounds, dipropylene glycol being present in a'major proportion of said mixture.

18. In the process of producing shaped articles from a polymeric spinning solution comprising an acrylonitrile polymer containing in the polymer molecule at least by weight of acrylonitrile and ethylene carbonate as a solvent for said polymer, the steps comprising, extruding said spinning solution into a liquid coagulating medium which, exclusive of the ethylene carbonate, consists essentially of a glycol compound selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 2-methylpentanediol-2,4, and mixtures of said glycols, said coagulating medium containing between about 10% and 30% by weight of ethylene carbonate; cooling at least a portion of said coagulating medium to a temperature between about 10 C. and

-20 0.; precipitating at least a portion of the ethylene carbonate present in said cooled liquid; centrifuging the resulting mixture under a centrifugal force between about 500 G and 2000 G; maintaining the precipitate in said centrifuge at a thickness between about one-half inch and three inches: returning a quantity of the resulting liquid to said coagulating bath suillcient to maintain the concentration of ethylene carbonate therein between about 10% and 30% by weight; rinsing said precipitate with water belo about 10 C. vwhile said precipitate is being centrifuged; dissolving additional quantities of said polymeric material with said rinsed ethylene carbonate precipitate to form said spinning solution; and repeating the cycle.

19. A process according to claim 18 in which the glycol compound is a mixture of said glycol compounds, dipropylene glycol being present in a ing distilled under vacuum major proportion of said mixture; and said water-rinsed ethylene carbonate precipitate beprior to dissolving additional quantities of the polymer therewith.

20. A process according to claim 19 in which said filtrate, prior to its return to the coagulatin; medium, is treated with activated carbon.

GERALD A. MCFARREN.

REFERENCES CITED The following references are of record in the I file of this patent:

UNITED STATES PATENTS 

1. IN THE PROCESS OF PRODUCING SHAPED ARTICLES FROM A POLYMERIC SPINNING SOLUTION COMPRISING AN ACRYLONITRILE POLYMER CONTAINING IN THE POLYMER MOLECULE AT LEAST 80% BY WEIGHT OF ACRYLONITRILE AND ETHYLENE CARBONATE AS A SOLVENT FOR SAID POLYMER, THE STEPS COMPRISING, EXTRUDING SAID SPINNING SOLUTION INTO A LIQUID COAGULATING MEDIUM COMPRISING EHTHYLENE CARBONATE AND A WATER-SOLUBLE, LIQUID, ALIPHATIC POLHYDRIC ALCOHOL COMPOUND; COOLING AT LEAST A PORTION OF SAID LIQUID COAGULATING MEDIUM TO A TEMPERATURE BELOW THAT AT WHICH THE ETHYLENE CARBONATE PRECIPITATES THEREFROM BUT ABOVE THE CONGEALING POINT OF THE POLYHYDRIC COMPOUND; PRECIPITATING AT LEAST A PORTION OF THE ETHYLENE CARBONATE PRESENT IN SAID COOLED LIQUID; SEPARATING THE PRECIPITATED ETHYLENE CARBONATE FROM THE COOLED LIQUID; RETURNING AT LEAST A PORTION OF THE RESULTING LIQUID TO SAID COAGULATING MEDIUM; AND REPEATING THE CYCLE. 